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Employing Fermi-LAT gamma ray observations, several independent groups have found excess extended gamma ray emission at the Galactic center (GC). Both, annihilating dark matter (DM) or a population of ∼ 10 3 unresolved millisecond pulsars (MSPs) are regarded as well motivated possible explanations. However, there is significant uncertainties in the diffuse galactic background at the GC. We have performed a revaluation of these two models for the extended gamma ray source at the GC by accounting for the systematic uncertainties of the Galactic diffuse emission model. We also marginalize over point source and diffuse background parameters in the region of interest. We show that the excess emission is significantly more extended than a point source. We find that the DM (or pulsars population) signal is larger than the systematic errors and therefore proceed to determine the sectors of parameter space that provide an acceptable fit to the data. We found that a population of order a 1000 MSPs with parameters consistent with the average spectral shape of Fermi-LAT measured MSPs was able to fit the GC excess emission. For DM, we found that a pure τ + τ − annihilation channel is not a good fit to the data. But a mixture of τ + τ − and bb with a σv of order the thermal relic value and a DM mass of around 20 to 60 GeV provides an adequate fit.

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We present results on searches for point-like sources of neutrinos using four years of IceCube data, including the first year of data from the completed 86 string detector. The total livetime of the combined data set is 1373 days. For an E −2 spectrum, the observed 90% C.L. flux upper limits are ∼10 −12 TeV −1 cm −2 s −1 for energies between 1 TeV and 1 PeV in the northern sky and ∼10 −11 TeV −1 cm −2 s −1 for energies between 100 TeV and 100 PeV in the southern sky. This represents a 40% improvement compared to previous publications, resulting from both the additional year of data and the introduction of improved reconstructions. In addition, we present the first results from an all-sky search for extended sources of neutrinos. We update the results of searches for neutrino emission from stacked catalogs of sources and test five new catalogs; two of Galactic supernova remnants and three of active galactic nuclei. In all cases, the data are compatible with the background-only hypothesis, and upper limits on the flux of muon neutrinos are reported for the sources considered.

An anomalous gamma-ray excess emission has been found in Fermi Large Area Telescope data 1 covering the centre of the Galaxy 2, 3 . Several theories have been proposed for this 'Galactic Centre Excess'. They include self-annihilation of dark matter particles 4 , an unresolved population of millisecond pulsars 5 , an unresolved population of young pulsars 6 , or a series of burst events 7 . Here we report on a new analysis that exploits hydrodynamical modelling to register the position of interstellar gas associated with diffuse Galactic gamma-ray emission. We find evidence that the Galactic Centre Excess gamma rays are statistically better described by the stellar over-density in the Galactic bulge and the nuclear stellar bulge, rather than a spherical excess. Given its non-spherical nature, we argue that the Galactic Centre Excess is not a dark matter phenomenon but rather associated with the stellar population of the Galactic bulge and nuclear bulge.The main challenge in pinning down the properties of the Galactic Centre Excess (GCE) is the modelling of diffuse Galactic emission from the interaction of cosmic rays with interstellar gas and radiation fields, by far the dominant source of gamma-rays in this region. The Fermi-Large Area Telescope (LAT) Collaboration designed a diffuse Galactic emission model based on a template 8 approach that is optimized to single-out gamma-ray point sources. This approach presupposes that the diffuse Galactic emission can be modelled as a linear combination of interstellar gas, inverse Compton maps, and several other diffuse components. Due to the limited kinematic resolution of gas tracers towards the Galactic Centre (GC), interstellar gas correlated gamma rays from the GC direction are difficult to disentangle. Previous studies 3, 4, 9 utilized interstellar gas maps that were constructed with an interpolation approach that assumed circular motion of interstellar gas. This kinematic assumption provides for an estimate of the distance to a part of the interstellar gas. However, it is well established that the Galaxy contains a central bar which causes non-circular motion of interstellar gas in its inner regions, so assuming circularity introduces a significant and avoidable bias to gamma-ray analyses of the GC region 10 .We use Fermi-LAT data accumulated between August 4, 2008 and September 4, 2015 in the 15 • ×15 • region around the GC. Hydrodynamical simulations 10 that account for the effects of the Galactic bar were used to better determine the diffuse Galactic gamma-ray emission. To evaluate the impact that the choice of interstellar gas models have on our results, we also constructed atomic and molecular hydrogen gas maps using an interpolation approach that reproduced those used in most previous gamma-ray analyses of the GC. We split each into 4 concentric rings, each with its own normalization parameter. Details of the model components and approach are provided in the Methods section.Interstellar gas map templates constructed using the results of hydrodynamical simulati...

Accurate measurement of neutrino energies is essential to many of the scientific goals of large-volume neutrino telescopes. The fundamental observable in such detectors is the Cherenkov light produced by the transit through a medium of charged particles created in neutrino interactions. The amount of light emitted is proportional to the deposited energy, which is approximately equal to the neutrino energy for ν e and ν µ charged-current interactions and can be used to set a lower bound on neutrino energies and to measure neutrino spectra statistically in other channels. Here we describe methods and performance of reconstructing charged-particle energies and topologies from the observed Cherenkov light yield, including techniques to measure the energies of uncontained muon tracks, achieving average uncertainties in electromagnetic-equivalent deposited energy of ∼ 15% above 10 TeV.

There is growing evidence that the Galactic Center Excess identified in the Fermi-LAT gamma-ray data arises from a population of faint astrophysical sources. We provide compelling supporting evidence by showing that the morphology of the excess traces the stellar over-density of the Galactic bulge. By adopting a template of the bulge stars obtained from a triaxial 3D fit to the diffuse near-infrared emission, we show that it is detected at high significance. The significance deteriorates when either the position or the orientation of the template is artificially shifted, supporting the correlation of the gamma-ray data with the Galactic bulge. In deriving these results, we have used more sophisticated templates at low-latitudes for the Fermi bubbles compared to previous work and the three-dimensional Inverse Compton (IC) maps recently released by the GALPROP team. Our results provide strong constraints on Millisecond Pulsar (MSP) formation scenarios proposed to explain the excess. We find that an admixture formation scenario, in which some of the relevant binaries are primordial and the rest are formed dynamically, is preferred over a primordial-only formation scenario at 7.6σ confidence level. Our detailed morphological analysis also disfavors models of the disrupted globular clusters scenario that predict a spherically symmetric distribution of MSPs in the Galactic bulge. For the first time, we report evidence of a high energy tail in the nuclear bulge spectrum that could be the result of IC emission from electrons and positrons injected by a population of MSPs and star formation activity from the same site. pulsars, in the form of either old "recycled" millisecond pulsars [13,18], or young pulsar remnants from Galactic Center supernovae [19,20]. The gamma-ray spectra of known pulsars are similar to the GCE, and the capture of pulsars onto the Galactic Center region by Globular Cluster disruptions could explain the GCE's quasi-spherical spatial distribution [21,22]. Other explanations for the GCE discussed in the literature include outbursts of cosmic-ray production by the central supermassive black hole (e.g., [23]).While pulsars are a natural astrophysical candidate, there is ongoing debate regarding the consistency of the luminosity function required to explain the GCE with that measured for the pulsar population observed elsewhere as point sources [24][25][26][27]. Nevertheless, there are strengthening indications that the GCE may have an astrophysical origin. Cosmic-ray interactions in the Galactic Center region are notoriously complex to model. New analyses have cast doubt on some of the main properties claimed previously for the GCE. First, the energy spectrum of the GCE is subject to large systematic uncertainties arising from the incomplete understanding of cosmic-ray interactions in the Galactic Center region (e.g., [13][14][15]17]). A variety of scenarios might, therefore, describe the GCE based on the energy spectrum alone. Second, it has been argued that the photon count distribution of the GCE is ...

The Fermi-LAT data appear to have an excess of gamma rays from the inner 150 pc of the Galactic Center. The main explanations proposed for this are: an unresolved population of millisecond pulsars (MSPs), dark matter (DM) annihilation, and nonthermal bremsstrahlung produced by a population of electrons interacting with neutral gas in molecular clouds. The first two options have spatial templates well fitted by the square of a generalized Navarro-Frenk-White (NFW) profile with inner slope γ = 1.2. We model the third option with a 20-cm continuum emission Galactic Ridge template. A template based on the HESS residuals is shown to give similar results. The gamma-ray excess is found to be best fit by a combination of the generalized NFW squared template and a Galactic Ridge template. We also find the spectra of each template is not significantly affected in the combined fit and is consistent with previous single template fits. That is the generalized NFW squared spectrum can be fit by either of order 1000 unresolved MSPs or DM with mass around 30 GeV, a thermal cross section, and mainly annihilating to bb quarks. While the Galactic Ridge continues to have a spectrum consistent with a population of nonthermal electrons whose spectrum also provides a good fit to synchrotron emission measurements. We also show that the current DM fit may be hard to test, even with 10 years of Fermi-LAT data, especially if there is a mixture of DM and MSPs contributing to the signal, in which case the implied DM cross section will be suppressed.